The goal of this project is to develop activated carbon (AC) amendment as a multifunctional, in-situ sediment remediation technique to reduce the bioavailability of both mercury (Hg) and polychlorinated biphenyls (PCBs) at contaminated sediment sites. Activated carbon particles will be impregnated with nanoscale zero-valent iron (nZVI) to induce Hg reduction and sequestration, and PCB dechlorination. Successful application of this innovative technology may significantly reduce the human health risks posed by Hg and PCBs at many hazardous waste sites, while minimizing negative impact to sensitive habitats. The project will accomplish its main goal through a combination of spectroscopic, physicochemical, and biological tests. State-of-the-art microspectroscopy will be used to understand contaminant binding to AC at the particle scale. Physicochemical tests will probe the partitioning of Hg and PCBs to AC particles, and provide insight into sequestration and dechlorination rates, including mechanistic understanding of the role of nZVI on these processes. Finally, biological tests with a relevant clam species will document the effectiveness of AC amendment in reducing Hg and PCB bioavailability to sediment-dwelling macro- invertebrates. Sediment from Stege Marsh (San Francisco Bay, CA), a toxic "hot spot" contaminated with both Hg and PCBs, will be used in these tests. In-situ treatment with (nZVI-) AC may protect sensitive habitats and endangered species, such as the California clapper rail in the case of Stege Marsh. Combined, Hg and PCB contamination are responsible for the vast majority of fish consumption advisories currently in effect in the US. In addition, public use of Hg- and PCB-contaminated sites is limited due to human health risks associated with these often co-occurring contaminants. This research advances AC amendment as a remediation strategy that will lower both types of human health risks by (1) reducing the level of Hg and PCBs entering the food chain, and (2) decreasing the availability of Hg and PCBs to the local environment.